51st ATF2 meeting

1. Layouts of Zero-Crossing Extraction, Feed-Forward Correction, and Fast Feedback Stabilisation at the ATF2, Alexander Kalinin (ASTEC Daresbury Laboratory CCLRC

Following three systems are explained in order to maintain the beam quality at ATF2. The first one is zero crossing system to extract beam when it cross the zero energy point in the energy oscillation in DR. Second, Feed Forward (FF) system has latency of 400ns from DR to EXT to correct transverse jitter in DR. Third, Feed Back (FB) has latency of 300 (150)ns to correct the extraction-kicker jitter.

Locations of elements are searched for based on the v3.6 optics (MAD). All of them are located at upstream of diagnostic section . Common elements of FF and FB are a pair of kickers with pickups and a pair of pickup in each direction of x and y, i.e. a pair for (x,x') or (y,y'). Kickers are 30cm long striplines and pickups are 15cm long stripline BPMs. Total length of a kicker with a pickup is 50cm including flanges. The optimum phase advance in a kicker pair or a pickup pair is 90 degree. One pickup (P3 in x ) is the same one at the first kicker (Ky1). So, there are 4 kickers and 7 pickups in total. All the pickups must have position resolution of 1um for small beta function .

For FF, there are two pickups in DR, which are stripline BPMs. Pickup 1 is downstream of Q6 in LQ6C (93.05m), pickup 2 is downstream of Q17 in LZV43 (115.63m)

For zero crossing (ZC), Orbit DR pickups are used: LRBPM13.9 and LRBPM2.28.

Finally, a FF/FB prototype is suggested for short cut to stabilize y only at the present EXT. It consists of a kicker and three BPMs. The kicker is placed downstream of QD8. BPMs are ML11, ML13 and ML14 for monitoring the extraction kicker jitter, feedback signal and witness, respectively. Performance of this prototype may be obscured by the extraction kicker jitter.

• Q : space of these elements are available ?
• A : Yes, they are placed in drift sections in the v3.6 optics .
• Q : Can DAL provide the components ?
• A : Yes, in principle.
• Q : Is any performance available ?
• A : No at present, however, the simulation could be done .
• Q : question on the horizontal FF/FB plan at ATF2; the system may not be effective since the kickers are placed at upstream of K2 (2nd kicker ) in your plan. In the double extraction kicker scheme, the first kicker(K1) makes large jitter, and the second one(K2) will compensate it .
• A : The extraction kicker is not important since the kicker effect is linear and the K1 and K2 are angle kickers .
• Q : Can you pass all the information of these systems to M.Woodley who is updating the device list based on the v3.7 optics ?
• A : Yes, I will.

2. Effect of Multi-Pole Component of QM7R on Emittance in ATF EXT, Shigeru KURODA (KEK)

First, he commented that the fitted multipole B fields, which has been presented by A.Seryi, should not be used to calculate the field felt by beam in DR for too large there.

He estimated emittance growth by each multipole components of 12, 10, 8 and 6 pole as a function of |x_o|< 1cm, |y_o| and &sigma_&delta < 0.1%, where x_o,y_o are position of extracted beam ( from the design orbit) and &sigma_&delta is momentum spread (RMS).

Results show very small effect on the emittance, while the 10 and 8 poles have slightly stronger dependence on x_o,y_o .

• Q : What is the coordinate origin ?
• A : the origin is the designed one
• Q : All components should be considered for combined effect.
• Q : Whais is definition of emittance ?
• A : It is projected one for thin lens approximation.
• Q : how well control of beam orbit ? How do we know and control the position ?
• A : It is very difficult to change the vertical position. how to measure the positions at very noisy positon ?
• Q : What is typical dispersion at the extraction ?
• A : No I can not say now.

3. Elegant vs MAD, Feng Zhou (SLAC)

Previously, the Elegant results have been presented for the ATF2-EXT-line simulations. Elegant can estimate the multipole effect only up to n=3, which might be enough for QM7, but the higher order components would significantly contribute at both QM7 and SepA. Therefore, new MAD tracking results were compared with the Elegant ones.

His summary is listed below;

• MAD can include multipoles n <,= 9, and proceed all corrections - orbit, dispersion, coupling and Twiss match.
• When beam is trapped in either horizontal or vertical off-center position at QM7 and SepA, no obvious vertical emittance growth observed after all corrections; same results as in elegant code.
• When beam is trapped in both horizontal and vertical off-center position (e.g., x=4mm and y=0.6mm) at QM7 and of course transversely offset at SepA, both horizontal and vertical emittance growths are obviously observed even after all corrections.
• Emittance growth slightly depends on the initial energy spread.
• All simulations are done on ATF2 EXT line; next is to simulate the existing ATF EXT line since both the EXTs are not fully identical.

• Q : Does the coupling come from higher order terms ?
• A : May be so, while the coupling corretion is linear.
• Q : What is emiitance growth ?
• A : 30% at least due to higher order correction
• A/C : It may be corrected by orbit bump, to make a knob to tune the orbit.
• Q : How much is emittance growth at the worst case ?
• Q : What are the emittance values before/after correction ?
• Q : What are the effects separately from QM7 and SepA ?
• A : There could be 7mm x -displacement in septum area of orbit correction. The displacement (offset) would generate multipole components at upstream of septum by kicker.
• Q : How do you determine the kick ?
• A : Just see the effect.
• Q : Do we expect 7mm offset ?
• A : Yes, simulation can tell some truth
• A : There are possible sources of trajectory error to see the effect. Horizontal orbit deviation can be large, but vertical one is difficult to deviate. We must estimate the vertical offset, anyway.

2. KEK site meeting ( in Japanese )

The next ATF2 meeting will be held on 18th July 2007, 2:30pm -, 3-gokan, 425, KEK, TV-ID#=31110 with the KEK Gatekeeper and ILC Webex.